The present invention is related to integrated circuits. More specifically, the present invention can be applied to controllers used for switch mode power supply. According to various embodiments, the present invention provides various power control schemes to reduce standby power consumption and improves system efficiency. Merely by way of example, the present invention can be used in switch mode power conversion system including, among, other things, offline fly-back converters and forward converters. It is to be appreciated that the present invention has a broad range of applications.
Power converters are widely used in various applications, such as providing power to portable consumer electronics. The power converters can convert electric power from one form to another form. As an example, the electric power is transformed from alternate current (AC) to direct current (DC), from DC to AC, from AC to AC, or from DC to DC. Additionally, the power converters can convert electric power from one voltage level to another voltage level.
In the past various types of power converters have been developed. For example, linear regulators have traditionally been used for power converters. A linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its “linear region” or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor. While linear regulators have been used for many years, their power efficiency is often inadequate for portable electronics. For example, due to low power efficiency, linear regulators often waste large amount of energy and generate excessive heat for portable devices.
With the advent of integrated circuits, switched-mode power supply has been invented and utilized for various applications. Switch mode power supplies are typically implemented with a switching regulator, which is an internal control circuit that switches the load current rapidly on and off in order to stabilize the output voltage. For certain applications, switch-mode power supply uses pulse-width-modulated (PWM) or pulse-frequency-modulated (PFM) mechanism. These mechanisms are usually implemented with a switch-mode-controller including various protection components.
In recent years, power systems are often required to comply with standards for energy consumption. For example, various international organizations have imposed energy saving standards such as “Energy Star”, “Blue Angel”, etc. For example, such standards impose requirements that, among other things, power supplies have low standby power consumption (i.e., high power efficiency under very light or zero load condition).
In the past various techniques have been developed to lower various forms of power consumption. For example, different types of standby power consumption schemes have been developed. Unfortunately, conventional techniques are often inadequate.
Therefore, it is desirable to have improved systems and methods for power systems.